diff --git a/coregrind/m_libcfile.c b/coregrind/m_libcfile.c
index 9ff6b61..d42128e 100644
--- a/coregrind/m_libcfile.c
+++ b/coregrind/m_libcfile.c
@@ -721,12 +721,7 @@
 }
 
 
-/* Create and open (-rw------) a tmp file name incorporating said arg.
-   Returns -1 on failure, else the fd of the file.  If fullname is
-   non-NULL, the file's name is written into it.  The number of bytes
-   written is equal to VG_(mkstemp_fullname_bufsz)(part_of_name). */
-
-Int VG_(mkstemp) ( HChar* part_of_name, /*OUT*/HChar* fullname )
+Int VG_(mkstemp) ( const HChar* part_of_name, /*OUT*/HChar* fullname )
 {
    HChar  buf[VG_(mkstemp_fullname_bufsz)(VG_(strlen)(part_of_name))];
    Int    n, tries, fd;
diff --git a/coregrind/pub_core_libcfile.h b/coregrind/pub_core_libcfile.h
index f27725b..d3bd680 100644
--- a/coregrind/pub_core_libcfile.h
+++ b/coregrind/pub_core_libcfile.h
@@ -95,9 +95,9 @@
 
 /* Create and open (-rw------) a tmp file name incorporating said arg.
    Returns -1 on failure, else the fd of the file.  If fullname is
-   non-NULL, the file's name is written into it.  The number of bytes
-   written is equal to VG_(mkstemp_fullname_bufsz)(part_of_name). */
-extern Int VG_(mkstemp) ( HChar* part_of_name, /*OUT*/HChar* fullname );
+   non-NULL, the file's name is written into it.  The number of bytes written
+   is equal to VG_(mkstemp_fullname_bufsz)(VG_(strlen)(part_of_name)). */
+extern Int VG_(mkstemp) ( const HChar* part_of_name, /*OUT*/HChar* fullname );
 
 /* Record the process' working directory at startup.  Is intended to
    be called exactly once, at startup, before the working directory